1. Field of the Invention
The present invention relates to a process for the preparation of phosphoric acid with concomitant recovery of compounds of fluorine and silica in solid form.
2. Description of the Prior Art
When phosphoric acid is produced by wet process, as is well known to this art, after the acid attack on the phosphate ore and filtration, the result is a phosphoric acid which has a level of P.sub.2 O.sub.5 concentration of from about 25 to 30%. Now, that acid is rarely used at such a level of concentration, in the various subsequent applications thereof.
Concentrations of from about 40 to 54% are generally required. Such, therefore, implies an acid concentration stage is required.
In the acid concentration operation, fluorides escape with the water vapor and, as it is not possible to discharge fluorine-charged vapors into the atmosphere, the vapors are treated with a liquid to absorb the fluorine compounds. That results in vapors from which fluorine has been removed and which can thus safely be discharged, and a solution of fluosilicic acid. The problem which arises, however, is that of finding use for the solution which also cannot be discharged, having regard to the fluorine content thereof.